linux-kernel - Re: [PATCH] nvme-pci: Make nvme_pci_npages_prp() __always

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Message-ID: <202505062255.130383D3B7@keescook>
Date: Tue, 6 May 2025 22:55:31 -0700
From: Kees Cook <kees@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Keith Busch <kbusch@...nel.org>, kernel test robot <lkp@...el.com>,
	Jens Axboe <axboe@...nel.dk>, Sagi Grimberg <sagi@...mberg.me>,
	linux-nvme@...ts.infradead.org, Chaitanya Kulkarni <kch@...dia.com>,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] nvme-pci: Make nvme_pci_npages_prp() __always_inline

On Wed, May 07, 2025 at 06:47:54AM +0200, Christoph Hellwig wrote:
> On Tue, May 06, 2025 at 08:35:40PM -0700, Kees Cook wrote:
> > The only reason nvme_pci_npages_prp() could be used as a compile-time
> > known result in BUILD_BUG_ON() is because the compiler was always choosing
> > to inline the function. Under special circumstances (sanitizer coverage
> > functions disabled for __init functions on ARCH=um), the compiler decided
> > to stop inlining it:
> 
> Can we place just fix um to still force inlining inline functions instead
> of needing these workarounds?

Oh, I don't have the history here. Is there something about UM and
forcing off inlining?

-- 
Kees Cook